GB2221578A - Waveguide apparatus - Google Patents

Abstract

Waveguide apparatus comprises two sections 1 and 2 forming a rectangular waveguide. Ridges 3 and 4 are included, being bisected by the mating surfaces of the two sections 1 and 2. Sandwiched between the two sections are two metallic fins 5 and 6 arranged parallel to the longitudinal axis of the waveguide, coplanar with the E-plane, and extending towards the centre. The fins may be formed on a dielectric substrate and a component such as a PIN diode may be connected across the gap between the fins. <IMAGE>

Description

WAVEGUIDE APPARATUS This invention relates to waveguide apparatus and in particular, but not exclusively, to hybrid E-plane waveguide apparatus.

The advent of modern transceiver technology has led to a new generation of microwave and millimetre wave systems, many using E-plane technology. E-plane technology is the use of devices in the E-plane (electric plane), of the waveguide which modify the chacteristics of the waveguide by their influence upon the electric field within it. This in turn modifies the characteristics of the resultant output signal.

The present invention arose in an attempt to provide improved waveguide apparatus which is particularly suitable for use with E-plane technology.

According to the invention, there is provided waveguide apparatus comprising a waveguide having a ridge extensive from an inner surface thereof; and a metallic fin extensive from the inner surface of the ridge and substantially perpendicular to the inner surface of the waveguide, the ridge and fin being extensive in the direction of the longitudinal axis of the waveguide.

Waveguide apparatus in accordance with the invention may give improved performance over conventional waveguide configurations. It enables the useable bandwidth to be increased.

The incorporation of the ridge within the waveguide effectively reduces the distance across the waveguide in the region of the ridge, therefore increasing the capacitance. By capacitively loading the waveguide in this way, the waveguide has a lower impedance and lower cutoff frequency. The incorporation of the ridge also concentrates the electric field within the waveguide at the point of closest separation between the ridge and oposite wall. This high field concentration at a particular region limits the number of modes possible within the guide and so, by correct positioning of the ridge, can limit unwanted waveguide modes1 these unwanted modes being known as overmodes. This therefore enables the waveguide to be used over a wider frequency bandwidth.

The addition of the fin further decreases the separation across the waveguide and because of the relative thinness of the fin compared with the other dimensions of the guide, can extend such as to leave only a narrow slot width across the waveguide enabling the frequency range between TElo cut on and TE20 overmode to be increased. By appropriate selection of the ridge and fin dimensions, the number of overmodes arising may be further reduced.

The main advantage of the fin is that by reducing the slot width1 a very low impedance is possible compared to that otherwise obtainable, and by the addition of the ridge either a lower impedance may be obtained, or alternatively, the same impedance can be obtained with a wider slot width facilitating construction.

Preferably, the section of the waveguide transverse to its longitudinal axis is substantially rectangular.

This enables the waveguide to function in only a limited number of given modes which is advantageous for the transmission of a signal along it. This reduces the possibility of overmodeswithin the required bandwidth.

Advantageously the ridge is also of substantially rectangular section transverse to the longitudinal axis and may be integral with the wall of the waveguide for ease of manufacturing. However, the ridge may be separate from the wall of the waveguide.

The ridge may be arranged such that its innermost surface is parallel to that of the facing wall of the waveguide. It thus functions as a parallel plate capacitance across the waveguide giving the maximum capacitance effect for a given surface area and the advantages associated with this as described above. The edges of the ridge may be radiussed to improve peak power handling and/or to ease interface with a normal ridge waveguide.

It is preferred that the fin lies along the centreline of the ridge and is substantially parallel to the longitudinal axis of the waveguide. Advantageously the fin is co-planar with the E-plane of the waveguide to achieve maximum interaction with the electric component of the electro-magnetic wave.

The fin may be a metallic layer which is supported by a dielectric substrate. This enables the fin to be insulated from the body of the waveguide if it is preferable to do so by ensuring only areas of the dielectric substrate come into contact with the waveguide.

Advantageously, the waveguide comprises two sections having mating surfaces co-planar with the E-plane of the waveguide to facilitate easier construction. It is preferred that part of the fin or substrate, where one is included, is sandwiched between the mating surfaces of the waveguide locating the fin in position.

In one preferred embodiment of the invention there is included a plurality of ridges arranged parallel to the longitudinal axis of the waveguide and each having a fin extensive from its inner surface. Advantageously at least one of said plurality of ridges is extensive from the inner surface of one of the waveguide walls, and another of said plurality is extensive from the inner surface of a facing wall. Preferably at least one ridge on one wall is directly opposite another ridge on a facing wall providing a slot at the centre of the waveguide co-planar with its E-plane.

Where each fin is to be supported by a dielectric substrate, a slot between them may advantageously be formed by photo-etching a thin strip of a metallic layer from the substrate so as to form two separate metalised surfaces. This technique enables a very narrow gap between the fins to be produced, providing a low impedance within the waveguide without the requirement for expensive CNCmachining or extruding of the waveguide.

A further advantage of the fins being on one substrate, is that it enables electrical components such as PIN diodes to be connected across the gap between opposite fins. This may be done prior to assembly of the fins within the waveguide, reducing the costs of manufacture.

Two embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a transverse sectional perspective view of waveguide apparatus in accordance with the invention; and Figure 2 shows a transverse sectional perspective view of a second embodiment of the invention.

Referring to Figure 1, a waveguide comprises two sections 1 and 2 which, when mated together, form a waveguide of rectangular cross-section perpendicular to the longitudinal axis of the guide. Two ridges 3 and 4 are extensive from the centre of opposite inner surfaces of the broad walls of the waveguide. The ridges are integral with the walls and are of rectangular crosssection perpendicular to the longitudinal axis of the waveguide and are bisected by the mating surfaces of sections 1 and 2.

Two metallic fins 5 and 6 are extensive from the innermost surfaces, 8, of the ridges towards the center of the guide being sandwiched between the mating surfaces of the sections 1 and 2.

Each fin is a thin rectangular member and is arranged between the sections 1 and 2 such that part of it extends into the waveguide cavity. The fins 5 and 6 are separated from each other by a distance 7 which is constant along the length of the waveguide.

Figure 2 depicts a waveguide arrangement similar to that of Figure 1 with like reference numerals for like parts. In this second example, the metallic fins 5 and 6 are formed upon a dielectric substrate 9. A second layer 10 of dielectric material is positioned between the fin 6 and the ridge 4 to insulate the fin 6 from the section 2 of the waveguide body. This dielectric may be an anodised layer.

A component 11, which may be a PIN diode for example, is connected across the gap 7 between the fins 5 and 6.

The fin may be connected to an external electrical circuit, not shown, which can function to either electrically bias the fin, or, if components are connected to the fin, either control the components, and thereby influence the output waveform of the waveguide, or obtain feedback from them enabling the performance of the waveguide to be monitored.

Claims (18)

1. Waveguide apparatus comprising a waveguide having a ridge extensive from an inner surface thereof; and a metallic fin extensive from the inner surface of the ridge and substantially perpendicular to the inner surface of the waveguide, the ridge and fin being extensive in the direction of the longitudinal axis of the waveguide.

2. Waveguide apparatus as claimed in claim 1 wherein the section of the waveguide transverse to its longitudinal axis is substantially rectangular.

3. Waveguide apparatus as claimed in claim 1 or 2 wherein the ridge is of substantially rectangular section transverse to the longitudinal axis.

4. Waveguide apparatus as claimed in any preceding claim wherein the fin lies along the centre-line of the ridge and is substantially parallel to the longitudinal axis of the waveguide.

5. Waveguide apparatus as claimed in any preceding claim wherein the fin is co-planar with the E-plane of the waveguide.

6. Waveguide apparatus as claimed in any preceding claim wherein the fin is a metallic layer which is supported by a dielectric substrate.

7. Waveguide apparatus as claimed in claim 6 wherein the fin is produced by etching of the metal from the dielectric substrate.

8. Waveguide apparatus as claimed in any preceding claim wherein the fin is in electrical contact with the ridge.

9. Waveguide apparatus as claimed in any of claims 1 to 7 wherein the metallic fin is electrically insulated from the ridge.

10. Waveguide apparatus as claimed in any preceding claim wherein the waveguide comprises two sections having mating surfaces co-planar with the E-plane of the waveguide.

11. Waveguide apparatus as claimed in claim 10, wherein part of the fin is sandwiched between the mating surfaces of the waveguide to locate it.

12. Waveguide apparatus as claimed in claim 10 wherein, where the fin is a metallic layer supported by a dielectric substrate, part of the dielectric substrate is sandwiched between the mating surfaces of the waveguide to locate it.

13. Waveguide apparatus as claimed in claim 10, 11 or 12 wherein the mating surfaces bisect the ridge.

14. Waveguide apparatus as claimed in any preceding claim and including a plurality of ridges arranged parallel to the longitudinal axis of the waveguide and each having a fin extensive from its inner surface.

15. Waveguide apparatus as claimed in claim 14 wherein at least one of said plurality is extensive from the inner surface of one of the waveguide walls and another of said plurality is extensive from the inner surface of a facing wall.

16. Waveguide aparatus as claimed in claim 15 wherein said at least one is opposite to said another.

17. Waveguide apparatus as claimed in claim 16 wherein an electrical component is connected across the gap between opposite fins.

18. Waveguide apparatus sunstantially as illustrated in and described with reference to Figure 1 or 2 of the accompanying drawings.